Many devices, such as cellphones, joysticks, remote controls with motion sensors, devices with sensors for measuring human movement intended for sporting or medical applications, or receivers for satellite navigation systems, use embedded sensors, such as magnetometers, accelerometers, or directional antennas (for measurements of directions of arrival or DOA). These sensors supply a measurement of a physical vector field that is generally substantially uniform in time and in space added to a bias or “offset”. By definition, the bias is the value read by the sensor in a zero field, i.e. when the physical field is zero. The use of the measured signal by the physical field sensor entails a conversion of the raw data into physical units by the application of a bias correction and sensor sensitivity parameters.
This bias can change abruptly or slowly over time. It does not depend on the physical field present in the environment (or ambient field), but on the sensor itself and/or on effects of the supporting device secured to the sensor. All of these effects, due to the sensor itself or to the device bearing the sensor are called endogenous (meaning endogenous to the device bearing the sensor), unlike the ambient field, called exogenous which is the object that is to be measured. To give an example of endogenous effect, the conditioning and conversion electronics of the sensor, the constituent mechanical or electronic elements of the device bearing the sensor, can be the source of the bias component. Some sensors also intrinsically exhibit a bias, which can be sensitive and variable as a function of temperature and/or of time. It can also be noted that the very step of manufacturing of the electronic board necessary for the device bearing the sensor, with its method for soldering the sensor onto the board, can modify the bias parameters of the sensor, for example by the application of mechanical stresses from the soldering step.